PROJECT SUMMARY/ABSTRACT Low-income adults in the US have historically had worse dental health outcomes including untreated caries rates at ~40% and less access to dental care than higher income individuals. Lack of or limited dental coverage among poor adults is thought to be an important factor for oral health disparities by income. Recently, 31 states and Washington DC expanded their Medicaid eligibility to all nonelderly adults with income below 138% FPL, with 24 of these states expanding on January 1 2014. These expansions have substantially increased Medicaid coverage among low income nonelderly adults including by nearly 10 percentage points in 2015. Twelve states of these expanding states are offering extensive dental coverage for the newly eligible adults, and another 11 states and DC are offering limited dental coverage. The Medicaid expansions in these states suggest that newly eligible adults have increased access to dental coverage and services. However, the extent to which the increased dental coverage have resulted in changes in access and use of dental services is an empirical question that has not been adequately addressed. Our goal in this study is to provide causal evidence on the effects of the recent Medicaid expansions in states offering extensive or limited dental coverage for the newly eligible low-income adults on use of dental preventive services and treatments over multiple years post the expansion. In addition to examining differences in effect by state Medicaid generosity of dental coverage, we will also evaluate differences in expansion effects by availability of dental care providers, since areas with more constrained dentist supply may experience smaller effects. We will employ quasi-experimental designs and nationally representative data to estimate these effects. The study findings will be of direct relevance for informing policymakers and other stakeholders about the effectiveness of the recent Medicaid expansions in modifying access to dental care and oral health outcomes among poor nonelderly adults and can be useful for future policies.